I don't know why SIGNIFICANT improvement is right.The negated answer is that traffic flow in and around cities is now so congested that significant improvement is impossible and in the argument there is no part to support 'significant' improvement.

So Eva's argument is not exclusively to directly improve traffic conditions and reduce accidents- it's at least partially a way to give drivers more information about traffic problems so they can choose other routes.

I just got C through process of elimination..

A- It doesn't matter if there still is a breakdown of vehicles, her system provides information in that event for alternate routes etc.B- Again, we don't necessarily need a "free flow of traffic" for the system to be effective.D- That's certainly not necessary- For all we know Eva is talking just about the city she lives in.E- Since "programmable highway signs" is mentioned in the text, we know that there are other ways than just having the vehicles fitted. So that's out.

Which leaves C. Look at the last line of what Eva says ("such a system, we can infer..."). If no improvement was possible, then her argument wouldn't work. I can see how "significant" is confusing, since degrees of improvement is not mentioned in what she said, but I think it just needs to be inferred.

Anyone else have any idea if the LSAT throws words such as "significant" in the right answer choice often?

You are right that the argument did not mention the term SIGNIFICANT. But not mentioning the term that way is characteristic of Necessary Assumption questions. And that is what makes Necessary Assumption questions tricky.

Every argument makes an enormous number of necessary assumptions. There will never be room to mention all the necessary assumptions that underlie an argument. And so you can’t expect that every term in the necessary assumption that is the correct answer-choice will be mentioned in the argument.

For instance, it is a necessary assumption of Eva’s argument that the “smart highway” system will be able to communicate with car computers well enough to be able to convey the traffic information in time for the drivers to use it. The argument also assumes that the “smart highway” system will be able to change the programable signs in time so that drivers are not working on old information. It further assumes that the programmable signs will be large and bright enough for the drivers to be able to see from the highway. It also assumes that the “smart highway” system’s way of collecting information about traffic congestion is reliable enough to provide information that is complete enough for drivers to use. And it presupposes that the drivers are not distracted by the “smart highway” system’s way of attracting their attention so that more accidents occur than would have occurred without the “smart highway” system. And, as you can see, you can just go on and on and on listing necessary assumptions.

What you did was exactly right. You found the one answer-choice that contained a necessary assumption.

And that the term SIGNIFICANT fits in. You can see that it is required when you leave it out. If you do that, then the necessary assumption of Eva’s argument is that the highway traffic congestion has not gotten so bad that it is now impossible to improve traffic flow. But what sort of improvement does Eva’s argument assume is still possible? Is it only a tiny insignificant improvement, such as allowing one worker to arrive at her work place 5 minutes earlier and in a slightly less angry mood? No, that can’t be right. Eva expects her proposal will result in significant improvement, not just a tiny trivial improvement.

The moral is, in Necessary Assumption questions, don’t expect the passage/stimulus to contain all the parts that compose the necessary assumption stated in the correct answer-choice. It is the nature of a necessary assumption to underlie the argument but not to be explicitly mentioned by the argument.

So Eva's argument is not exclusively to directly improve traffic conditions and reduce accidents- it's at least partially a way to give drivers more information about traffic problems so they can choose other routes.

I just got C through process of elimination..

A- It doesn't matter if there still is a breakdown of vehicles, her system provides information in that event for alternate routes etc.B- Again, we don't necessarily need a "free flow of traffic" for the system to be effective.D- That's certainly not necessary- For all we know Eva is talking just about the city she lives in.E- Since "programmable highway signs" is mentioned in the text, we know that there are other ways than just having the vehicles fitted. So that's out.

Which leaves C. Look at the last line of what Eva says ("such a system, we can infer..."). If no improvement was possible, then her argument wouldn't work. I can see how "significant" is confusing, since degrees of improvement is not mentioned in what she said, but I think it just needs to be inferred.

Anyone else have any idea if the LSAT throws words such as "significant" in the right answer choice often?

Now I understand why C is the correct answer. Thank you for your help!!

You are right that the argument did not mention the term SIGNIFICANT. But not mentioning the term that way is characteristic of Necessary Assumption questions. And that is what makes Necessary Assumption questions tricky.

Every argument makes an enormous number of necessary assumptions. There will never be room to mention all the necessary assumptions that underlie an argument. And so you can’t expect that every term in the necessary assumption that is the correct answer-choice will be mentioned in the argument.

For instance, it is a necessary assumption of Eva’s argument that the “smart highway” system will be able to communicate with car computers well enough to be able to convey the traffic information in time for the drivers to use it. The argument also assumes that the “smart highway” system will be able to change the programable signs in time so that drivers are not working on old information. It further assumes that the programmable signs will be large and bright enough for the drivers to be able to see from the highway. It also assumes that the “smart highway” system’s way of collecting information about traffic congestion is reliable enough to provide information that is complete enough for drivers to use. And it presupposes that the drivers are not distracted by the “smart highway” system’s way of attracting their attention so that more accidents occur than would have occurred without the “smart highway” system. And, as you can see, you can just go on and on and on listing necessary assumptions.

What you did was exactly right. You found the one answer-choice that contained a necessary assumption.

And that the term SIGNIFICANT fits in. You can see that it is required when you leave it out. If you do that, then the necessary assumption of Eva’s argument is that the highway traffic congestion has not gotten so bad that it is now impossible to improve traffic flow. But what sort of improvement does Eva’s argument assume is still possible? Is it only a tiny insignificant improvement, such as allowing one worker to arrive at her work place 5 minutes earlier and in a slightly less angry mood? No, that can’t be right. Eva expects her proposal will result in significant improvement, not just a tiny trivial improvement.

The moral is, in Necessary Assumption questions, don’t expect the passage/stimulus to contain all the parts that compose the necessary assumption stated in the correct answer-choice. It is the nature of a necessary assumption to underlie the argument but not to be explicitly mentioned by the argument.